Known wheel bearings of the type shown in FIGS. 1 and 2, and indicated generally at 10, have a stationary outer hub 12, which is secured to a non illustrated vehicle suspension, and a rotatable spindle, indicated generally at 14. Spindle 14 rotates because it carries the vehicle wheel 16, as well as a brake drum 18. Brake drum 18 is mounted to spindle 14 through an open, central circular hub 20, which has a predetermined axial thickness as measured between a pair of circular edges. The inner edge, indicated at 22, appears to be a sharp comer in cross section, and is generally referred to as the "theoretical sharp comer." Adequate clearance from the comer is important to the proper installation of the brake drum 18 to spindle 14. Specifically, spindle 14 includes a cylindrical pilot 24 with an outer surface over which the brake drum hub 20 is inserted, with a very close radial clearance. A flat annular wheel flange 26 radiates outwardly from the pilot 24, perpendicular thereto, with a flat outboard outer surface 28 against which the brake drum hub 20 is abutted, and an axially opposed inboard outer surface 30. The brake drum hub 20 is firmly sandwiched between the outboard abutment surface 28 and the wheel 16 itself, which is bolted onto conventional studs 32, when the vehicle is operating. In addition, small clips on the studs 32 can be used, if desired, to retain the brake drum hub 20 flat against the flange abutment surface 28 when the vehicle is stationary and the wheel 16 is removed. There is little need for such retainers, however, because of the close fit of hub 20 over the pilot 24, and such clips would be primarily needed during shipping, when the bearing 10 and brake drum 18 would be handled as a unit.
The primary concern relative to brake drum 18 is not shipping retention, but rather the maintaining of a close, flat to flat contact of the hub 20 against the wheel flange abutment surface 28 during vehicle operation. This assures the clean and efficient translation of braking loads on drum 18 to the spindle 14 and, ultimately, to wheel 16. To that end, a relief channel 34 is machined into both the outer surface of pilot 24 and the wheel flange abutment surface 28 at their circular, perpendicular juncture. Relief channel 34 is machined when the other critical surfaces, such as the pilot 24, are machined to final dimension on the initial blank from which spindle 14 is manufactured, which itself is forged to near net shape. Other structural features of spindle 14, such as the holes for the studs 32, are cut through the blank with dies. The existence of relief channel 34 at the point where the "theoretical sharp corner" represented by the edge 22 lies assures that, regardless of any tolerance variations in the edge 22, there will not be any physical interference that could potentially hold the surface of brake drum hub 20 away from the wheel flange abutment surface 28. However, the juncture between pilot 24 and the wheel flange 26 is critical for another reason. The stress of wheel loads on flange 26 tend to bend and flex it about its juncture with pilot 24, although the spindle flange 26 is made more than thick enough not to actually bend or crack significantly in actual operation. Nevertheless, if deliberately stressed to failure in a test fixture, such stresses will naturally concentrate in a predictable zone that finds the "weakest link", which is the effectively least thickness between the pilot 24-abutment surface 28 juncture and the opposed, inboard wheel flange surface 30. Such deliberately caused high stress will cause a crack to form through this stress zone, which is shown as a diagonal dotted line in FIG. 2, but represents, in fact, a conical surface. The necessary relief channel 34 does round out the otherwise sharp juncture between pilot 24 and flange 26, which tends to avoid stress concentration. More significantly, however, machining out the steel that creates the relief channel 34 significantly thins the flange 26 at the very point where stresses will concentrate, and thereby necessitates that flange 26 be thicker and heavier than it would otherwise have to be. Heat treating the surface of channel 34, as by induction methods, would harden it, but represents an additional and expensive step which is generally not done, in preference to just making flange 26 thick enough that the thinning created by the channel 34 is not a problem. While spindles like 14 do and have operated very successfully, it is a constant goal to improve designs and methods of manufacture so as to save weight and cost.